As the health care law takes a pounding from Republicans on Capitol Hill and from Republican governors across the country, Obama administration officials are trying to calm concerns that states won’t have the flexibility they need to implement a key part of the the sweeping measure.

An administration memo circulating Thursday details how states can determine which insurers will be allowed to offer plans in the “exchanges,” marketplaces established in 2014, where eligible individuals can purchase health care coverage. The memo also discusses how states can tailor Medicaid plans to “mirror options available in the private market, such as a standard Blue Cross/Blue Shield plan or a state employee health plan.”

The guidance also states that the exchanges can also offer a GOP favorite — health savings accounts, where consumers can put money tax-free to help pay for medical costs.

“Make no mistake: the State-based health insurance exchanges called for in the Affordable Care Act will give states substantial flexibility to establish exchanges that meet the unique needs of their residents,” the document reads.

In the adminstration’s continued effort to defend and promote the law, Department of Health and Human Services Secretary Kathleen Sebelius, in an op-ed published in The Washington Post, said the law “already gives states most of the resources and flexibility they’re asking for,” and that the measure “gives states incredible freedom to tailor reforms to their needs.”

The administration’s moves come after 21 Republican governors wrote to Sebelius Monday to ask for specific changes to the law. Indiana Gov. Mitch Daniels also weighed in via an op-ed – in The Wall Street Journal he wrote that “the law expects to conscript the states as its agents in its takeover of health care. It assumes that we will set up and operate its new insurance ‘exchanges’ for it, using our current welfare apparatuses to do the numbingly complex work of figuring out who is eligible for its subsidies, how much each person or family is eligible for, redetermining this eligibility regularly, and more.”